In the manufacture of optical fiber, the glass rod from which the fiber is drawn is formed using a multi-step process. First and second glass tubes, known as exhaust tubes, are each held in place via a lathe machine equipped with a heat torch. One end of a hollow glass tube, or a hollow quartz tube, which may be known as a starter tube, is fused to one end of the first exhaust tube. The opposite end of the starter tube is fused to one end of the second exhaust tube. Typically, the exhaust tubes are a) approximately 2 inches in diameter and b) larger than the starter tube. The difference in size between the exhaust tubes and the starter tube requires that the end of each exhaust tube that is fused to the starter tube be tapered in order to match the diameter of the starter tube. More precisely, it is preferable that the exhaust tubes each be shaped to narrow at a prescribed angle, e.g., 90°, 1) to facilitate a good connection between the ends of the starter tube and the ends of the exhaust tubes, and 2) to insure proper rotation of the combined tubes in the lathe machine.
Once the exhaust tubes and the starter tube are fused together, the starter tube is heated while gas is pumped from one side of the lathe machine into the end of the first exhaust tube that is not fused to the starter tube. The gas exits the first exhaust tube at the fused end, flows through the starter tube, then flows through the second exhaust tube, flowing from its fused end to its free end, and ends at the opposite end of the lathe machine. The heating of the gases solidifies the starter tube. After six to eight hours of heating in the presence of flowing gas, the starter tube is cooled until it becomes a solid rod. The ends of each exhaust tube that are fused to the solid rod are cut to remove the solid rod, and the solid rod is processed further to become optical fiber.
An optical fiber manufacturing plant that operates, for example, 100 lathe machines 24 hours per day, using 2 exhaust tubes per lathe machine per solid rod, with a 6 to 8 hour cycle time to manufacture a solid rod, requires 600 to 800 exhaust tubes per day. Recycling the exhaust tubes so that they may be reused lowers the number of new exhaust tubes that are needed per day, as well as the overall cost of manufacturing optical fiber. Although a short portion of the exhaust tube is lost when the rod is removed, the remaining portion may be recycled and repeatedly reused until the length after separation from the rod is insufficient to function as an exhaust tube.
The process of recycling exhaust tubes begins by making a second cut near the edges of each exhaust tube to remove any portions of each exhaust tube that may contain contaminates and discoloration from the heating and gases used to manufacture the solid rod. The angle of the cut is very important, because failure to cut the exhaust tube at a perpendicular angle will prevent a good connection from being made between the exhaust tube and the next starter tube to which the exhaust tube will be fused, rendering the exhaust tube unusable. Disadvantageously, presently, the determination of how much of each exhaust tube should be cut, along with the actual cutting, is performed by a person. After being properly cut, it must be determined whether the remaining length of exhaust tube is sufficient for reuse. Also, each exhaust tube must be inspected to insure that it is undamaged and may be reused. Disadvantageously, the measuring and inspecting steps are also performed manually. Manually measuring and cutting often results in too much of the exhaust tube being cut, thereby reducing the size of the exhaust tube that remains for future reuse, and resulting in the premature discarding of reusable exhaust tubes.
The remaining portions of reusable exhaust tubes are transported, e.g., by a person using a cart, to a processing area to be cleaned. The cleaning process should remove any contaminates and discoloration that were not cut off and remain after the manufacture of the solid rod. The cleaning is, disadvantageously, a manual process. Typically, it takes between 5 and 10 minutes to complete the cleaning of an exhaust tube. During the cleaning, each exhaust tube is soaked in a chemical mixture, scrubbed by hand with a steel brush, rinsed, and then scrubbed again by hand to remove any chemical residue. Further, disadvantageously, the cleaning process involves the use of chemicals that are harmful to humans if inhaled.